The present invention relates generally to electric-powered vehicles and particularly to a hydraulic system for such vehicles giving priority to the steering system of the vehicle over the implement or work system.
Vehicles such as lift trucks and the like, which are used in warehouses and similarly enclosed areas, are normally electric-powered. The power for such vehicles is normally supplied by storage batteries which are charged when the vehicle is not in use and supply sufficient power for the vehicle to operate over an extended period of time.
Such vehicles normally employ a hydraulic system for the implements of the vehicle such as the lift forks, and in most cases employ a hydraulic powered steering system. The pump for the hydraulic system is normally powered by means of an electric motor separate from the electric motor that powers the vehicle. Because of the extended intervals of time in which the implements of the vehicle may not be in use, a system is provided for automatically cutting off the motor of the hydraulic system of the vehicle when not in use in order to conserve electric power of the storage batteries. However, vehicles having power steering, when in operation, require almost constant and frequent minor corrections in the steering of the vehicle. For this reason a substantially constant supply of fluid for the steering system is essential.
Also, because of the different pressure requirements between the implement circuit and the steering circuit, a problem exists when the same circuit or source of fluid is utilized for both systems. Separate systems are impractical because of the cost involved and because of the required space on the vehicle for such a separate system.
Another problem with such systems is arranging the system to provide a ready availability of pressure for either of the implement or the steering circuit on demand. The main problem is providing a system wherein fluid is readily available for the steering system and wherein neither of the systems that is, the steering circuit or the implement circuit, will interfere with one another. When circuits having systems such as a power steering system and an implement manipulation system are supplied with pressure from the same hydraulic system, because of the diverse requirements of the system they may generally interfere with one another.